Theoretical and experimental techniques are used to develop a bonding model for the interaction of metalloporphyrins with small molecules (CO, NO, O2). This model is utilized in the recognition of behavior unique to hemeproteins. Heme model complexes are then designed and synthesized to emulate specific structural or electronic features of hemeproteins as one method of revealing factors essential to protein function. A series of O2, NO, and CO complexes with iron (II), (III), cobalt (II) (III) and manganese(II)(III) have been prepared and are being characterized by electronic, vibronic, and epr spectroscopy. These new porphyrin complexes are being crystallized for X-ray structure determination. Heme protein model systems are being prepared by introducing side chains onto protoporphyrin IX which can intramolecularly bind the iron heme site. Nitrogen heterocycles are used in modeling myoglobin-type heme proteins and mixed nitrogen and sulfur donors are used in modeling cytochromes c and P450. BIBLIOGRAPHIC REFERENCES: B.B. Wayland, M.E. Abd-Elmageed, and L.F. Mehne, "Low-Spin Cobalt(II)-Schiff Base and -Porphyrin Complexes of CO. MeNC, AsMe3 and PX3. Electron Paramagnetic Resonance Studies", Inorg. Chem., 14, 1456 (1975). B.B. Wayland, L.W. Olson, and Z.U. Siddiqui, "Nitric Oxide Complexes of Manganese and Chromium Tetraphenylporphyrin", J. Amer. Chem. Soc., 98.1, 94, (1976).